A great and versatile database schema illustrating e-commerce items as well as their rates management is needed.

To be sure with Chris Roberts, OSCommerce is a great starting point in addition to DatabaseAnswers.org.

Hope that can help.

I am sure you will find many good examples about - try searching at some free shopping cart software tools.

Like a general point, though, I believe you will find a lot of ways in which an item prices and discount / gift voucher system could work that getting a database schema that actually works for every possibility is not likely!

Possibly it can save you a little misery by refining the needs just a little?